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Dental microwear reflects the abrasiveness of foodstuffs consumed by extant primates and it is commonly used to trace dietary adapta-tions in fossil hominins. However, the impact of feeding events and ecological constraints on micro-scale tooth wear formation processes remain unclear. Here, we use dental buccal-mi-crowear analysis to test age-related effects of physical food processing on tooth-use in a natu-rally accumulated skeletal assemblage from the well-documented population of mountain gorillas from Volcanoes National Park, Rwanda. We analyzed dental microwear pattern of single teeth belonging to individual skeletons: 14 decid-uous m2 (aged 1.2-6.08 years) and 39 permanent molars (~90% M2) of adult gorillas (10.69-44.55 years, 25 males and 14 females). Our results indicate that adult gorillas present more abraded molar buccal surfaces, with significantly higher densities and longer micro-striations, than imma-ture individuals, which reflects the abrasive potential of ingested foods and the micro-stria-tion cumulative process. However, we also found that dental buccal-microwear variability was not associated with age when only adult gorillas were considered. Thus, gorillas from this popula-tion present a stable microwear pattern through adulthood, despite intraindividual variability in feeding ecology. Our findings show the cumulative process of dental buccal-microwear as immature mountain gorillas increase their intake of solid foods and develop an adult diet; but also, the stability of this pattern when diet over time is stable. We confirm that dental buccal-microwear variability is a reasonable proxy for feeding ecology in primates, although seasonality, habitat variability and diet proportions at individual level should be considered in future studies. 

Mountain gorillas are particularly inbred compared to other gorillas and even the most inbred human populations. As mountain gorilla skeletal material accumulated during the 1970s, researchers noted their pronounced facial asymmetry and hypothesized that it reflects a population-wide chewing side preference. However, asymmetry has also been linked to environmental and genetic stress in experimental models. Here, we examine facial asymmetry in 114 crania from three Gorilla subspecies using 3D geometric morphometrics. We measure fluctuating asymmetry (FA), defined as random deviations from perfect symmetry, and population-specific patterns of directional asymmetry (DA). Mountain gorillas, with a current population size of about 1000 individuals, have the highest degree of facial FA (explaining 17% of total facial shape variation), followed by Grauer gorillas (9%) and western lowland gorillas (6%), despite the latter experiencing the greatest ecological and dietary variability. DA, while significant in all three taxa, explains relatively less shape variation than FA does. Facial asymmetry correlates neither with tooth wear asymmetry nor increases with age in a mountain gorilla subsample, undermining the hypothesis that facial asymmetry is driven by chewing side preference. An examination of temporal trends shows that stress-induced developmental instability has increased over the last 100 years in these endangered apes.